Many subsea fields on the NCS are now entering maturity. As reservoir pressure declines, this inherently introduces significant well construction and well delivery challenges. Wells are the biggest driver for increased recovery. Depletion and increased formation pressure heterogeneity in mature fields are driving costs and slowing well delivery. For fields developed with fixed platforms, conventional pressurized Managed Pressure Drilling (MPD) techniques developed on land has been used for some time to combat these challenges. For floaters with subsea Blow Out Preventers (BOPs) and Low pressure marine drilling risers in harsh environment, other technologies are needed. EC-Drill is a new technology developed by AGR Enhanced Drilling specifically for floaters which will regulate the drilling fluid level in the marine riser in order to manage the wellbore pressures. A subsea mud pump is connected to the marine drilling riser and is used to manage the fluid level within the riser up or down. The drilling fluid is pumped back to surface from a lower level on the riser so that the hydrostatic pressure in the wellbore can be managed more effectively. This also enables using conventional mud weight to drill depleted reservoirs. The technique also allows for precise control of wellbore pressures and enables drilling with close to constant bottom hole pressure. The technology will ensure improved hydraulics which can result in; improved hole cleaning, higher rate of penetration, improved casing/liner cementing, less downtime (NPT) due to formation pressures heterogeneity and longer horizontal sections may now be drilled in depleted reservoirs, etc.
This paper discusses the challenges related to drilling in depleted reservoirs and outline the new drilling technique that is available to solve these and other drilling challenges on the Norwegian Continental Shelf (NCS).